The above referenced application describes a memory system in which a word of data is stored across two or more asynchronous memory devices such as disk drives. For example, each of the bits in a thirty-two bit word of data and a seven bit error correction code is stored in a different one of thirty-nine disk drives.
The error correction code that is associated with each word stored in the memory system makes it possible to detect up to two bits of error in a word read from the memory system and to correct one bit of error. As a result, it is possible to operate the memory system even if one of the disk drives is inoperative. Thus, for each word, the bit that would otherwise have been read from the inoperative disk drive is calculated from the information in the other bits of the word and the error correction code that are read from the other disk drives.
This, however, only represents a temporary solution because in such circumstances the entire system is vulnerable to an error in any additional bit. Accordingly, it is desirable to replace the inoperative disk drive as expeditiously as possible. Replacement of a disk drive, however, and in particular replacement of the data stored in the disk drive, is a relatively time consuming task with even the most sophisticated disk drives because of their large capacity.